The Unity system was devised by architects Kendrick, Findlay and Partners.
An early design was used for probably under 100 houses in the 1947-48 period, then a re-design was used to build possibly 3,000 houses between 1948 and 1950. A further re-design in 1950 was used for – the next 10 years to build the bulk of the 19,000 Unity dwellings constructed.
There are a number of properties at Great Shelford which are of the latter type and are classified as the ‘B’ type variant.
Foundations consist of a concrete strip footing.
The load bearing elements in a Unity house consist of storey height, reinforced concrete columns of 3 1/2″ x 6″ cross section, at 3′ 0″ centres around the house perimeter. The earlier design has columns with an indentation in the sides, giving a dumbbell shaped cross section. However, the later columns, like those at Great Shelford, are of rectangular cross section.
Columns are connected by cold-formed steel bracing. Ground floor columns are longer than those at higher levels and have a boot shaped projection at one end. During construction, the boot ends of the ground floor columns were stood on the footing. Typically, the spaces between the columns were in-filled with masonry to retain fill below the ground floor structure. On some sites, it has been known to infill the spaces between the columns with mass concrete. The columns form window reveals and mullions.
Walls are clad with stack bonded, unreinforced concrete panels just under 3′ 0″ long and 11″ high, with a clinker block-work inner leaf. Panels have shaped, interlocking upper and lower edges to reduce rain penetration. Façade panels are tied back to columns by copper straps. These hook onto wires cast into the backs of the panels at one end and are fixed to the side of the columns at the other. Front faces of the columns are treated with bitumen to form a vertical damp proof course between column and cladding.
Generally, the clinker block-work inner leaf is rarely continuous through the floor void, being supported at each floor level. Tying of the inner leaf to the columns is more primitive than that for the outer leaf. Typically, nails are partially driven into timber plugs cast into the rear face of the columns, hopefully aligned with the bed joints in the block-work, and built into the wall. Unity houses of the post 1950 type have distinctive square comer panels, which typically are only held in place by steel wire in the bed joints, embedded in generally poor quality concrete infilling in the void behind.
The ground floor is of solid concrete construction. The first floor is formed from 4″ deep steel joists, spaced at 3′ 0″ intervals. The floor is finished with tongue and grooved floor-boarding, nailed to timber joists that are notched into the webs of the steel joists.
The roof is of timber trussed rafter construction, lined with felt and battens and clad with interlocking tiles. 5.6.6 Other The party wall construction comprises two leaves of 2 1/2″ clinker block-work separated by a 2 1/2″ cavity. Load-bearing spine walls are generally of masonry construction, although in some variants there is a load-bearing PRC beam spanning the opening between the lounge and dining room. Internal partitions are typically of clinker block-work or masonry construction with a hard plastered finish. Ceilings are formed with plasterboard. Chimneys are of masonry construction.
Unity House PRC Repair Video Selection